There's been a recent dust-up in the micro and home-brewing worlds involing Bell's Two Hearted Ale and a homebrew kit from Northern Brewer called Three-Hearted Ale. The problem for Bell's is simply the name. Bell's doesn't seem to mind that it's intended to be a clone of their beer.
As for Northern, they and their supporters seemed to be miffed that Bell's didn't just call and ask them nicely to stop, but sent a letter written by a lawyer instead.
Here are some links on the issue: